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From "Andrei Dulceanu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OAK-6678) Syncing big blobs fails since StandbyServer sends persisted head
Date Wed, 27 Sep 2017 13:46:00 GMT

    [ https://issues.apache.org/jira/browse/OAK-6678?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16182583#comment-16182583
] 

Andrei Dulceanu commented on OAK-6678:
--------------------------------------

bq. What do you think about that?
[~frm], I agree with all your proposals, except the part below:

{quote}
The 1s on the server, given the implementation in the patch, translates to eight consecutive
attempts at reading the head state IIUC.
{quote}
I think an improved default for timeout on the server is >5s (e.g. 6s), since the flush
thread kicks in once every 5s. This way we really use the "read persisted head with retry"
mechanism, by waiting for the flush thread to actually write the latest content to segments.

{quote}
The timeout should be part of the configuration of the StandbyServer
{quote}
I agree, but one question comes to mind: what do we do with existing OSGi setting {{standby.readtimeout}}?
Do we split it into two settings, one for the server, defaulting to 6s (let's say), to be
used while fetching the persisted head state and one for the client, to be used while waiting
for a response from the server?

On a different note, one important gain from treating the absence of a persisted head state
on the primary as a non-erroneous behaviour, is the fact that we will be able to start two
instances (primary and standby) and let them do the sync in multiple cycles, without worrying
about what's flushed on the primary.

> Syncing big blobs fails since StandbyServer sends persisted head
> ----------------------------------------------------------------
>
>                 Key: OAK-6678
>                 URL: https://issues.apache.org/jira/browse/OAK-6678
>             Project: Jackrabbit Oak
>          Issue Type: Bug
>          Components: segment-tar, tarmk-standby
>            Reporter: Andrei Dulceanu
>            Assignee: Andrei Dulceanu
>              Labels: cold-standby, resilience
>             Fix For: 1.8, 1.7.9
>
>         Attachments: OAK-6678-02.patch, OAK-6678.patch
>
>
> With changes for OAK-6653 in place, {{ExternalPrivateStoreIT#testSyncBigBlog}} and sometimes
{{ExternalSharedStoreIT#testSyncBigBlob}} are failing on CI:
> {noformat}
> org.apache.jackrabbit.oak.segment.standby.ExternalSharedStoreIT
> testSyncBigBlob(org.apache.jackrabbit.oak.segment.standby.ExternalSharedStoreIT)  Time
elapsed: 96.82 sec  <<< FAILURE!
> java.lang.AssertionError: expected:<{ root = { ... } }> but was:<{ root : {
} }>
> ...
> testSyncBigBlob(org.apache.jackrabbit.oak.segment.standby.ExternalPrivateStoreIT)  Time
elapsed: 95.254 sec  <<< FAILURE!
> java.lang.AssertionError: expected:<{ root = { ... } }> but was:<{ root : {
} }>
> {noformat}
> Partial stacktrace:
> {noformat}
> 14:09:08.355 DEBUG [main] StandbyServer.java:242            Binding was successful
> 14:09:08.358 DEBUG [standby-1] GetHeadRequestEncoder.java:33 Sending request from client
Bar for current head
> 14:09:08.359 DEBUG [primary-1] ClientFilterHandler.java:53  Client /127.0.0.1:52988 is
allowed
> 14:09:08.360 DEBUG [primary-1] RequestDecoder.java:42       Parsed 'get head' message
> 14:09:08.360 DEBUG [primary-1] CommunicationObserver.java:79 Message 'get head' received
from client Bar
> 14:09:08.362 DEBUG [primary-1] GetHeadRequestHandler.java:43 Reading head for client
Bar
> 14:09:08.363 WARN  [primary-1] ExceptionHandler.java:31     Exception caught on the server
> java.lang.NullPointerException: null
> 	at org.apache.jackrabbit.oak.segment.standby.server.DefaultStandbyHeadReader.readHeadRecordId(DefaultStandbyHeadReader.java:32)
~[oak-segment-tar-1.8-SNAPSHOT.jar:1.8-SNAPSHOT]
> 	at org.apache.jackrabbit.oak.segment.standby.server.GetHeadRequestHandler.channelRead0(GetHeadRequestHandler.java:45)
~[oak-segment-tar-1.8-SNAPSHOT.jar:1.8-SNAPSHOT]
> {noformat}



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